The present invention relates to an organic EL (electro-luminescence) display device and a method for manufacturing the same.
The present application claims priority from Japanese Application No. 2002-323552, the disclosure of which is incorporated herein by reference.
An organic EL display device shows images on an arrangement of organic EL elements, each of which works as a unit of a light-emitting element. Each organic EL element is constructed as follows; a transparent electrode of ITO or the like is formed to serve as an anode on a transparent glass substrate or the like, on which organic layers including a light-emitting layer are formed of organic compounds, furthermore on which a metallic electrode of Al or the like is formed as a cathode.
In such an organic EL display device, each functional element such as a Thin Film Transistor (hereinafter referred to as TFT) necessary for active-matrix driving or a color filter or the like for multi-color display is firstly formed on the substrate. In order to flatten an irregular (concavo-convex) surface resulting from the formation of these functional elements, an underlying layer is then formed on the entire substrate, on which each organic EL element is further formed at the location corresponding to that of an individual functional element.
A specific example of a conventional organic EL display device is disclosed, for example, in Japanese Patent Application Laid-Open No. 2001-356711, in which TFTs are formed on a substrate serving as the above-mentioned functional elements for driving individually the organic EL elements formed in a dot-matrix arrangement. The formation of TFTs and wiring layers connected to them cause the concavo-convex surface, hence a flattening layer of resin material or the like becomes necessary in order to flatten the concavo-convex surface. Furthermore, because gas components, such as moisture, emitting from the flattening layer are possible to deteriorate the organic EL element, a passivation layer is formed as a gas-barrier to prevent its deterioration, on the flattening layer. The organic EL elements, furthermore, are formed on the passivation layer.
In another conventional example, Japanese Patent Application Laid-Open No. Hei. 11-121164 discloses that color filters or color-converting filters for multi-color display are formed for serving as the above-mentioned functional elements on a substrate. Furthermore, multi-layered flattening layers of resin materials are formed in order to fill and flatten the concavo-convex surface resulting from the formation of the color filters or the color-converting filters. A passivation layer is further provided on the flattening layer, and then the organic EL elements are formed on the passivation layer.
Such an organic EL display device typically provides the underlying layer including the flattening layer or the passivation layer on the entire surface of the substrate. A simple matrix-driving display device, for example, has connecting regions on the peripheral region of the substrate, for connecting leading electrodes of each organic EL element with electrodes of peripheral circuits or driving ICs. At each connecting region, the leading electrode drawn out on the above-mentioned underlying layer is interconnected to a Chip On Flexible Printed Circuit (COF) or the like.
The COF is equipped with the driving ICs on a Flexible Printed Circuit (FPC), and a Tape Carrier Package (TCP) equipped with the IC chips by using a Tape Automated Bonding (TAB) is typically adopted. The interconnection of the TCP electrode and the leading electrode is made by thermocompression bonding of these electrodes sandwiching an anisotropic conductive film (ACF) between them. It is known that failure in the interconnection tends to occur when the leading electrode is formed on the underlying layer of organic materials such as resin or the like. This is because the underlying layer can no longer perform as a supporting base for the leading electrode due to a thermo-deterioration of the underlying layer caused by heating at the thermocompression bonding, hence the thermocompression bonding of the electrodes with the anisotropic conductive film therebetween can not be done sufficiently. More specifically, it is necessary to form at least one layer, which is formed of organic materials, in the underlying layer for flattening the concavo-convex surface on the substrate. However, because a heat-resistance critical temperature of the organic materials is substantially equal to the temperature (180° C.–200° C.) of the thermocompression bonding, the heat-deterioration of the underlying layer is inevitable as a result thereof. A reliable connection is thus hard for the thermocompression bonding of the leading electrodes on the underlying layer.
This problem is not restricted only to the connection to the COF, but the similar problems occur also in the case of the Chip On Glass (COG) equipped with the IC chips to leading electrodes above a substrate. That is, the COG employs a thermocompression bonding of an electrode of an IC chip and a leading electrode, sandwiching an anisotropic conductive film (ACF) between the two electrodes. When the bonding is performed to the leading electrode formed on the underlying layer, the heat-deterioration of the underlying layer is inevitable, so that a reliable connection may fail.